1. Field of the Invention
The present invention relates to a color conversion apparatus for converting image data in which a color of pixels constituting an image is represented by coordinate values in a first color space into image data in which the color of the pixels is represented by coordinate values in a second color space, and a color conversion program storage medium storing a color conversion program for converting image data in which a color of pixels constituting an image is represented by coordinate values in a first color space into image data in which the color of the pixels is represented by coordinate values in a second color space.
2. Description of the Related Art
There is known various types of input devices for obtaining image data through input of an image, for example, a color scanner for reading a recorded image to obtain image data and a digital still camera (DSC) in which image data is obtained in such a manner that an image of a subject is formed on a solid state imaging device and then read. In those input devices, the image data is represented by data of a predetermined range of for example 0 to 255 on each of three colors for example red (R), green (G) and blue (B). Colors, which can be represented by numerical values in the predetermined range on each of those three colors of R, G and B, are restricted as a matter of course. For this reason, even if colors of the original image have very plentiful representation, conversion of the colors into image data once using such an input device causes an image represented by the image data to be restricted to the colors in a certain color representation area in the R, G and B color space.
Also with respect to an output device for outputting an image in accordance with image data, there are known various types of output devices, for example, a photographic printer in which a printing paper is exposed by a laser beam to develop the printing paper so that an image is recorded on the printing paper, a printer in which an image is recorded on a sheet in accordance with a system such as an electrophotographic system and an inkjet system, a printing machine in which a rotary press is rotated to create a number of printed matters, and an emissive display device such as a CRT display and a plasma display in which light is emitted on a display screen in accordance with image data to display an image. Also with respect to an output device, similar to the above-mentioned input device, there exists a color reproduction area according to the associated output device. That is, the output device is able to represent various colors in accordance with for example image data representative of three colors of R, G and B or image data representative of four colors of C (cyan), M (magenta), Y (yellow) and K (black). However, colors, which can be represented, are restricted to a certain color representation area (for example, a color representation area represented by numerical values of a range of 0 to 255 on each of colors of R, G and B) in an output device color space (for example, an RGB space and a CMYK space).
Even if a certain image data (for example, data representative of (R, G, B)=(50, 100, 200)) is concerned, a color of an image, which is obtained in accordance with such image data, is varied depending on a sort of an output device. Regarding this point, it is the same between an input device and an output device. Even if image data (R, G, B)=(50, 100, 200), which is obtained by a certain input device, is used as it is, and an image is outputted by a certain output device, a color of an image outputted from the output device is not coincident with a color of the original image entered through the input device. Accordingly, when it is intended that the original image is reproduced by a certain output device in accordance with image data obtained through reading an image by a certain input device, there is a need to convert the image data but not directly sending the image data obtained in the input device to the output device. Here, there is performed a conversion paying attention to a color of an image, and a conversion of such image data is referred to as color conversion. A LUT (Lookup table) or the like defining a relationship between image data before and after the color conversion is referred to as a color conversion definition (a color profile). Creating the color conversion definition (a color profile) is referred to as a profiling. The color conversion definition defines the association between coordinate values of two color spaces.
As mentioned above, a color representation area is varied in accordance with a device, and colors to be represented in the respective devices are different from one another even if image data is concerned with the same numerical value. On the other hand, recently, it is desired to construct a device independent type of system capable of incorporating therein a plurality of sorts of input devices and a plurality of sorts of output devices, wherein the input devices and the output devices are connected to one another. In such a device independent type of system, to perform the color conversion between the devices, there is adopted a scheme in which a common color space (a space of a device independent data) independent of a device, for example, an L*a*b* color space, is interposed, so that a color conversion for converting image data on a color space depending on an input device, which is obtained by the input device, into image data on the common color space, and a color conversion for converting the image data on the common color space into image data on a color space depending an output device are performed. In the device independent type of system, as the above-mentioned color conversion definition (a color profile), there are created an input profile defining a color conversion between a color space depending on an input device and a common color space, and an output profile defining a color conversion between a color space depending on an output device and the common color space.
By the way, in order to obtain a natural tone of image in the event that an output device outputs an image represented by image data that is obtained through photography of a camera subject such as a person and a scenery, there is a need to apply a data processing of altering a tone of an image to the image data in addition to the above-mentioned color conversion.
On the other hand, in the event that an output device outputs an image represented by image data that is obtained through reading of a photographic print and a printed matter, it is desired that the above-mentioned color conversion is applied to the image data, and a color of the image such as the photographic print and the printed matter is reproduced as it is.
For this reason, in the event that a plurality of sorts of input devices is incorporated into a device independent type of system that is the usual system, it is necessary for a user to confirm the contents of image data to decide whether the data processing is needed. This is troublesome and very inconvenient.